In the optical transmission system, as one of factors to limit the power of light input to the optical fiber, Stimulated Brillouin Scattering (SBS) occurs, which then causes backscattering of a part of the input power and this may adversely affect the transmission system. Conventionally, the technique of suppressing the SBS include: (1) electrically controlling a light source; and (2) optically controlling a light source. The technique (1) is electrical modulation such as frequency modulation, amplitude modulation and dither, which is disclosed in U.S. Pat. No. 5,329,396 December 1994 Fishman et al. The technique (2) relates to control of an optical spectrum using nonlinear phenomenon of an optical fiber, such as Cross-Phase modulation (XPM) and Self-Phase Modulation (SPM), which is particularly effective to pulse light and disclosed in Y. Horinouchi et al., “Stimulated Brillouin Scattering suppression effects induced by cross-phase modulation in high power WDM repeaterless transmission”, Electron Lettr., Vol. 34, No. 4, pp.390-391, (1998) and U.S. Pat. No. 6,516,113 B1 April 2003 Glingener et al.
Besides, in recent years, a demand for large-capacity in the optical signal transmission system has been increased. In response to this demand for the large capacity, attempts are being made to achieve terabit capacity of the basis transmission system. This terabit transmission system can be achieved mainly by wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM). The former is a system such that a plurality of signals of different wavelengths is multiplexed to be transmitted as a single signal and the latter is a system of enhancing optical transmission speed (transmission capacity per unit time) itself.
In the optical transmission system using these systems, there is a method of using a repeater for regenerating a signal in an optical area not electrically in the transmission line (optical regeneration). In such optical regeneration, a report has been made as shown in the following Table 1.
TABLE 1mode-lockedfiber lasermode-locked laserdiode(5)required(1) active(2) passive(3) active(4) passiveLD + EAMspec.repetition-rate<40 GHzM~GHz<40 GHz>10 GHz<40 GHz>10 GHztemporal>sub-ps<sub-ps>sub-ps>sub-ps>ps<psdurationtiming jitterlowlargelowlargelowlowstabilitylowlowhighhighhighhighsynchro.easynot easyeasyeasyeasyeasy
The systems (1), (3) and (5) shown in Table 1 are based on electrical signal modulation, while the systems (2) and (4) are based on the all-optical technique which needs no electrical circuit. The system (1) is disclosed in M. Nakazawa and E. Yoshida, IEEE Photon. Technol. Lett., 12, 1613 (2000), (2) in K. Tamura et al., Opt. Lett., 18, 1080 (1993), (3) in H. Kurita et al., IEICE Trans. Electron. E81-C. 129 (1998)., (4) in K. Sato, Electron. Lett., 37, 763 (2001) and (5) in H. Kawatani et al., OFC2001, MJ3-1 (2001).
Further, as a system other than those shown in Table 1, there is proposed a system of converting dual-frequency light into a soliton pulse train by a soliton compression fiber (E. M. Dianov et al., OL, 14 1008(1989)).
Furthermore, in order to realize high-speed signal transmission, there is a technique of utilizing a light source for generating a high-bit-rate optical signal. One example of this technique is an optical pulse compressor using adiabatic soliton compression, which is disclosed in “Picosecond soliton pulse-duration-selectable source based on adiabatic compression in Raman Amplifier” (R. C. Reeves-Hall et al, Electron. Lett., 2000, Vol. 36, pp.622-624).
From the description made up to this point, the present invention has an object to provide a light source having an SBS suppressing effect in optical communication and also a downsized and configurationally simple waveform shaper, an optical pulse train generator and an optical regenerating system.